This invention relates to an arrangement for measuring or determining the quiescent current of an integrated monolithic digital circuit, which arrangement comprises a current sensor for measuring (sensing) the quiescent current, which is provided with a first connection terminal for coupling to a supply terminal of the integrated monolithic circuit and with a second connection terminal for coupling to a supply.
The invention further relates to an integrated monolithic digital circuit provided with such a current measuring arrangement.
The invention moreover relates to a testing apparatus provided with such an arrangement.
An arrangement for measuring a quiescent current of an integrated monolithic digital circuit is known from the article "Built-In-Current Testing-Feasibility Study", W. Maly and P. Nigh, Proceeding ICCAD 1988, pp. 340-343, IEEE. In this publication, testing of digital VLSI circuits by means of a current sensor incorporated in the integrated monolithic circuit is described. The current sensor has a non-linear characteristic, more particularly the current sensor is a bipolar transistor having an exponential I-U characteristic, is. The current sensor is included between the monolithic circuit and the supply of the monolithic circuit and serves to measure abnormal quiescent currents which are due, for example, to shortcircuits and/or floating gate electrodes of, for example, MOS-FET's in the VLSI circuit. The measurements are made dynamically, that is to say that test vectors are supplied at inputs of the VLSI circuit and the quiescent current is measured in rest periods between switching operations. If the VLSI circuit operates satisfactorily, the quiescent current can be orders of magnitude smaller as compared with an unsatisfactory operation. A quiescent current measurement can therefore give an indication about a satisfactory or an unsatisfactory operation of the VLSI circuit. The voltage across the current sensor is compared with a reference voltage in quiescent current periods. If the voltage is larger than a predetermined value, the VLSI circuit is very likely to be defective. Because of the exponential characteristic of the transistor, it is possible to discriminate between a comparatively large current during switching of transistors in the VLSI circuit and the comparatively small quiescent currents. In the prior arrangement, a bipolar current sensor is used in a MOS environment, which may give rise to problems with respect to integration in the same integrated monolithic digital circuit. Further, a satisfactorily operating VLSI circuit, in which a current sensor is included, will operate more slowly than a VLSI circuit without a current sensor.